1. Field of the Invention
This invention relates to a method of recovering unreacted monomers from an effluent stream of an olefin polymerization process. More particularly, the invention relates to a cyclic method of recovering unreacted monomers by the adsorption and subsequent desorption thereof and the recycle of the monomers to the reactor.
2. Description of the Prior Art
Polymers and copolymers of C.sub.2 -C.sub.10 olefins, particularly copolymers of ethylene and higher alpha-olefins, have in recent years been produced in gas phase, fluid bed reactors. Karol et al, U.S. Pat. No. 4,302,566, describe a gas phase, fluid bed reactor for producing linear low density polyethylene polymers. Graff, U.S. Pat. No. 4,173,547, Stevens et al, U.S. Pat. No. 3,787,384, Strobel et al, U.S. Pat. No. 4,148,754 and Ziegler, deceased, et al, U.S. Pat. No. 4,063,009, describe various polymerization processes which produce polyethylene other than linear low density polyethylene.
Nowlin et al, U.S. Pat. No. 4,481,301, teach the preparation of a highly active alpha-olefin polymerization catalyst, and a polymerization process utilizing the catalyst, comprising contacting a support material, e.g., silica, containing reactive OH groups with a stoichiometric excess of an organomagnesium composition, and subsequently treating the product with a tetravalent titanium compound.
Bobst et al, U.S. Pat. No. 4,372,758, disclose a process for removing unpolymerized monomers from alpha-olefin polymers, comprising introducing an inert gas into a purge vessel countercurrently to the flow of the polymer product also introduced into the purge vessel. The unreacted hydrocarbon monomers are stripped from the product in the purge vessel, a vent gas containing the monomers is recovered from the purge vessel, a portion of the vent gas is burned in a flare, and the remainder thereof is recycled to the purge vessel as a conveying stream for the polymer or as a purge stream.
Yamaguchi et al, U.S. Pat. No. 3,989,881, disclose a solid catalytic complex for the polymerization of olefins comprising magnesium and a metal halide, wherein the metal is titanium or vanadium, and a cyclic or an aliphatic ether. The catalyst is used in the polymerization of alpha-olefins to produce polymers having relatively high bulk density.
The entire contents of all of the above-discussed patents are incorporated herein by reference.
As is known to those skilled in the art, in olefin, especially alpha-olefin, polymerization processes the product polymers, i.e., resins, contain some unreacted hydrocarbon monomers, e.g., see Bobst et al, discussed above. For economic, safety and environmental reasons, the unreacted hydrocarbon monomers are removed from the resins before they are stored in shipping containers. One of the heretofore-practiced methods of removing the monomers involved stripping thereof from the product in a purge vessel, thereby generating a vent gas containing the monomers. The vent gas was removed from the purge vessel and it was either burned in a flare or, at least a portion thereof, was recycled to the purge vessel as a conveying stream for the polymer or as a purge stream (see the aforementioned patent to Bobst et al).
However, a need still exists in the art for providing a more energy efficient and relatively low cost method of removing unreacted hydrocarbons, such as monomers, from the vent gas of an olefin polymerization process.